US ambassador Susan Rice says her government will attempt to restore the reference to sexual orientation. Photograph: Kevin Wolf/AP

A culture war has broken out at the UN over whether gay people should be offered the same protections as other minorities whose lives are threatened.

The issue will come to a head today when the general assembly votes on renewing its routine condemnation of the unjustified killing of various categories of vulnerable people.

It specifies killings for racial, national, ethnic, religious or linguistic reasons, and includes refugees, indigenous people and other groups.

But because of a change promoted by Arab and African nations and approved at committee level, the resolution drops "sexual orientation" and replaces it with "discriminatory reasons on any basis".

The US government says it is incensed at the change, as are gay rights campaigners. "Even if those countries do not support gay rights, you would think they would support our right not to be killed," said Jessica Stern of the New York-based International Gay and Lesbian Human Rights Commission.

Stern said gay people all over the world were frequent targets of violence because of their sexual orientation.

Authorities in Jamaica are investigating a possible hate crime after the killing of a man who belonged to the country's sole gay rights group, earlier this month.

Uganda, among 76 countries that criminalise homosexuality, is debating whether to join the five other countries that consider it a capital crime.

The biennial resolution does not refer to sexual orientation for the first time since 1999. The US ambassador, Susan Rice, said she was "incensed" that the reference was removed, and that the US will attempt to restore it.

The battle underscores the historic split over gay rights among UN members and their diverse religious and cultural sensibilities.

Activists say gay and lesbian issues got only minimal attention at the UN a decade ago.

"There has been slow but steady progress on lesbian, gay, bisexual and transgender rights at the UN," Stern said.

Stern cited as progress UN secretary general Ban Ki-moon's "landmark" speech during a gay rights forum at UN headquarters on Human Rights Day, 10 December, calling for an end to laws around the world that make it a crime to be homosexual.

But as gay rights gain more acceptance in the UN system, some member states are pushing back, said Mark Bromley, of the Washington-based Council for Global Equality, which aims to advance gay rights in American foreign policy. "I think some states are uncomfortable and they are organising to limit engagement on the issue."

"We are seeing a backlash," agreed Stern. "This is an illustration of the tensions around culture at the United Nations, and how power plays out and alliances are made."

On behalf of African countries, Benin introduced the amendment that deleted the sexual orientation reference. The largely Christian country of eight million with a sizeable Muslim population argued that "sexual orientation had no legal foundation in any international human rights instruments".

Morocco, an Arab country that is almost exclusively Muslim, asserted that such selectivity "accommodated particular interests and groups over others" and urged all UN member states "to devote special attention to the protection of the family as the natural and fundamental unit of society".

Western nations opposed the move to delete the mention of sexual orientation. Britain called it "an affront to human dignity", while France and Norway said the move was "regrettable".

The amendment was passed at a committee meeting last month by 79-70, with 17 abstentions.

General assembly resolutions are not legally binding, but rather reflect the views of the majority of the world's nations.

Mark Kornblau, spokesman for the US mission to the UN, said the US will introduce an amendment next week to restore the previous language, including the phrase "sexual orientation" because "this is an issue that is important to us".

Gay groups and human rights activists also have been lobbying missions to the UN in New York in recent days, urging in particular, the delegations that abstained on the amendment to help restore the mention of sexual orientation.

"We only need a few more countries and we can change this vote around," said Boris Dittrich of Human Rights Watch.

But gaining the world's support for gay rights will take far longer.

More than two-thirds of UN members, many of them Muslim nations, are refusing to sign a separate UN statement condemning human rights violations based on sexual orientation and gender identity, especially with regard to the application of the death penalty and extrajudicial, summary or arbitrary executions.

Under the Bush administration in 2008, the US refused to join all other western nations in signing the declaration, arguing that the broad framing of the language in the statement might conflict with US laws.

After Barack Obama took office last year, the US joined other member states to support the declaration, saying it found that the language did not conflict with American laws. Sixty-eight of the UN's member countries have now signed the declaration, and 124 countries have abstained.